This invention relates to safety valves for relieving excessive pressure in fluid systems to avoid equipment damage and personal injury. More specifically, this invention relates to an improved valve disc and a safety valve employing the disc to improve valve seat tightness in certain similar contemporary safety valve designs.
Pressure relief or safety valves are employed in operating systems for generating, controlling, and utilizing fluids such as saturated and superheated steam. Typical of such safety valves is a huddling chamber type of valve which has been marketed for a number of years. Such valves include a nozzle for admitting steam into the valve from a pressure vessel. A valve seat is formed on the discharge end of the nozzle in a chamber of the main body of the valve. The nozzle is closed to prevent steam escape by a valve member generally referred to as a "valve disc" which is movable relative to the nozzle seat and biased to a closed position on the seat by a compression spring. When the steam pressure in the vessel exceeds a predetermined value, the valve disc is forced from the nozzle seat to admit steam from the pressure vessel into the valve chamber from which the steam flows through an outlet leading from the chamber. When the pressure in the vessel drops to a predetermined level the compression spring forces the valve disc back on the nozzle seat closing the safety valve. The difference between the pressure at which the valve opens and the pressure at which the valve recloses is often referred to as "blowdown". The ratio of the pressure at which the valve begins to leak or simmer to the opening pressure of the valve is referred to as "seat tightness". For example, a valve having a set opening pressure of 500 psi which starts to simmer or leak at 480 psi has a seat tightness of 96%.
Valves of the general type of the present invention are illustrated and described in the following United States Patents: U.S. Pat. No. 4,708,164 for SAFETY RELIEF VALVE, issued to David J. Scallan, Nov. 24, 1987; U.S. Pat. No. 4,858,642 for IMPACT RESISTANT PRESSURE RELIEF VALVE, issued to John E. Fain, Jr., Aug. 22, 1989; and U.S. Pat. No. 5,234,023 for PRESSURE RELIEF VALVE WITH AUXILIARY LOADING DEVICE, issued to Ying-San Lai, Aug. 10, 1993. More specifically, valves of the type of the present invention are 1500 SERIES SAFETY VALVES manufactured and marketed by Dresser Industries, Industrial Valve Operation, Dresser Valve and Controls Division, and described and illustrated in Bulletin SV-7. published by Dresser Industries in July, 1986. The 1500 SERIES VALVES utilizes a THERMOFLEX valve disc.